This invention relates to improvements in hydraulic systems for agricultural implements and to control and drive systems for same.
Air seeders typically comprise a seeding implement and a product carrying aircart. Sometimes additional implements such as a packer are operated in combination with air seeders. Hydraulic systems for aircarts with hydraulic fan drives have large power demands which can be in excess of what a tractor hydraulic system can properly provide. This can be more of a problem when the air seeder is used in combination with other implements having hydraulic systems.
A boost system which provides additional fluid power for aircarts is shown in the related patent specification "Hydraulic System Having Boost Pump in Parallel with a Primary Pump And Boost Pump Drive Therefor" of Russell J. Memory et al. In the Memory et al system the tractor primary pump and a boost pump are arranged in parallel in a hydraulic circuit to supply an aircart fan motor. Flow controls for the system enable one pump to maintain at least a minimum flow to the load when the flow provided by the other pump diminishes. The boost system increases total fluid capacity so that reserve capacity for serving other loads is maintained. In the Memory et al specification prior art related to such hydraulic systems is presented and the benefits of the Boost Pump parallel system are described. The parallel system, however, has some shortcomings which the present invention overcomes.
As noted above, the Memory et al parallel boost system provides additional fluid volume to maintain the aircart fan operation when the tractor primary hydraulic system is insufficient. However, the speed at which the aircart fan operates is also limited by the pressure provided to it. Demand for increased sizes of air seeders requires aircart fans to provide more airflow to deliver the seeding products farther distances across the larger implements.
One prior art system is disclosed in the article titled White Hydraulics PTO Pump System" appearing in Design News, Jul. 20, 1992. The system shown in that article is one in which a tractor system operates as a charge pump for a PTO driven hydraulic pump. The circuit shown is not a series boost system but, rather, the tractor system provides only a charge pressure as is required by gerotor pumps. The circuit shows that the pressure across the motor is the difference between the charge pressure and the PTO pump pressure and the circuit is not a series boost pressure circuit.